2025 NYJC H2 Chem Hydroxy Compounds Tut Ans SECTION A.pdf

1 Nanyang Junior College Chemistry (9729) Tutorial 14 Hydroxy Compounds Prepared by Mrs Judy Tan JC2/2025 Section A: Self-Check Questions Part 1: Alcohols 1 For the following compounds given by their IUPAC name, draw their skeletal formula. (i) Propan-1,3-diol OH OH (ii) Phenylmethanol OH 2 Below is a cyclohexane derivative. OH State the type of reaction and draw the structural formula of the organic product(s) formed by the action of the reagents stated below: (a) HCl (g) (b) Acidified dichromate(VI) ions CH3 Cl Type of reaction: nucleophilic substitution CH3 O Type of reaction: oxidation (c) Na metal (d) Concentrated H2SO4 at 170oC CH3 O - Na + Type of reaction: reduction CH3 CH3 (major) (minor) Type of reaction: elimination

2 3 There are four structural isomers of C4H9OH. The structure of one isomer, 2-methylpropan-2-ol, a tertiary alcohol is shown below. HO C CH3 CH3 CH3 (i) Draw the structures and give the names of the other three isomers of C 4H9OH. Classify each as either primary, secondary or tertiary. isomer CH3CH2CH2CH2OH CH3CH(OH)CH2CH3 CH3 C CH3 CH2 OHH name butan-1-ol butan-2-ol 2-methylpropan-1-ol classification primary secondary primary (ii) One of the isomers gives a positive test with alkaline aqueous iodine. Identify the isomer and write a balanced equation for the reaction. The isomer is CH3CH(OH)CH2CH3, (butan-2-ol). CH3CH(OH) CH2CH3 + 4I2 + 6NaOH  CHI3 + CH2CH3CO2Na+ + 5NaI + 5H2O (iii) 2-methylpropan-2-ol could be distinguished from the other two isomers by a simple chemical test. State the test and give the observations. test: To each sample, add potassium dichromate(VI), H2SO4 (aq) and heat Observations: 2-methylpropan-2-ol (Tertiary alcohol): Orange potassium dichromate(VI) remains Butan-1-ol & butan-2-ol: Orange potassium dichromate(VI) turns green Continue on the next pg

3 (iv) One of the isomers of C4H10O exhibit the following:  It exists as a pair of isomers.  3 alkenes are formed when it is heated with Al2O3. Identify the alcohol, including your reasoning. The alcohol is CH3CH(OH)CH2CH3. (butan-2-ol)  It exists as a pair of enantiomers as it contains a chiral carbon. C CH2CH3 CH3 OH H C CH2CH3 CH3OH H  It undergoes elimination with Al2O3 to form the 3 alkenes: C C H H H CH2CH3 C C H CH3 H CH3 C C CH3 H H CH3 But-1-ene cis but-2-ene trans but-2-ene

4 4 Complete the following summary of reactions for a secondary alcohol, propan-2-ol. (Compare this summary with the one for a primary alcohol – pg 20 of notes, how are reactions of a primary and secondary alcohol different?) propan-2-ol halogenoalkane SOCl2, room temp. Na , room temp. CH3CH2COOH, conc. H 2SO4, heat under reflux or CH3CH2COCl, room temp. K2Cr2O7, H 2SO4 (aq) heat under reflux I2 (aq), NaOH (aq), warm excess conc H2SO4 at 170O